The invention relates to air control in fluidic containers. More specifically it relates to using an evacuated structure to remove air accumulated in a fluid container.
After initial filling of a fluid container such as an ink-jet printhead, care is taken to eliminate air bubbles. Later, unwanted air can be introduced into or formed within the fluid container. For instance, with ink-jet cartridges, air bubbles may be introduced when carried in the ink supplied to the pen. Further, air is often diffused with the fluids. Heat, either by ambient temperature or generated by use of the fluid container cause dissolved air within the fluid to form air bubbles within the container. Such air bubbles do not readily re-dissolve back into the fluid when the fluid cools. Air is also drawn into the pen through either orifices used to remove fluid from the containers or slowly through the material that container is made from.
Unwanted air can cause several problems. For instance, in ink-jet printheads, the unwanted air can lead to print quality problems. An air bubble can obstruct ink flow to particular firing chambers from which ink droplets are to be ejected. Air bubbles can cause irregularly shaped ink droplets or cause a printhead to deprime resulting in complete failure of the printhead. Further, the air bubbles can form larger pockets of air that affect the operation of the printhead.
Air present in fluid containers, such as ink containers and printhead cartridges, can interfere with the maintenance of negative pressure often referred to as back-pressure. During environmental changes, such as temperature increases and ambient pressure drops, the air inside a fluid container will expand in proportion to the total amount of air contained within the container. This expansion is in opposition to the internal mechanism (a back-pressure regulator) that maintains the negative pressure. The internal mechanism within the printhead can compensate for these environmental changes only over a limited range of environmental excursions. Outside of this range, the pressure in the fluid container will become positive thereby causing fluid to be expelled from the container. A need exists to prevent unwanted air from affecting the contents of fluid or other containers.
An evacuated structure removes air accumulated within a container that contains material held at a first pressure. The evacuated structure has a shell that includes a slowly defusing air-permeable material. The air permeable material interfaces to a volume of space evacuated to a second pressure less than the first pressure within the container. Unwanted air that accumulates within the container is drawn into the volume of space of the evacuated structure due to the difference in pressure between the interior of the container and the interior of the shell.